Air batteries typified by a lithium air battery are batteries which uses oxygen as the cathode active material to discharge. The basic structure of air batteries comprises an anode, an air cathode (cathode) and an electrolyte present between the anode and air cathode. The cathode active material, oxygen, is obtained from the air and is not needed to be encapsulated in the battery. Therefore, air batteries can increase the anode active material amount per unit volume larger than batteries in which the cathode active material in solid form is encapsulated. Accordingly, air batteries have large electrical capacity and can be made smaller and lighter, easily. Also, oxygen has the advantage that it is not a limited resource. As just described, air batteries have many advantages and are expected to be used as batteries for portable devices, hybrid vehicles, electric vehicles, etc. Examples of air batteries include lithium-air, magnesium-air and zinc-air batteries.
An air battery comprises, for example, an air cathode layer containing an electroconductive material, catalyst and binder, an air cathode current collector for collecting current from the air cathode layer, an anode layer made of metal or alloy, an anode current collector for collecting current from the anode layer, and an electrolyte present between the air cathode and anode layers.
For example, in an air battery in which each of the migrating ions is a monovalent metal ion M+, it is thought that the following charge and discharge reactions proceed:
[Upon discharge]
                Anode: M→M++e−        Cathode: 2M++n/2O2+2e−→M2On [Upon charge]        Anode: M++e−→M        Cathode: M2On→2M++n/2O2+2e−        
Examples of electrolytes include non-aqueous electrolytes in which a supporting electrolyte salt is dissolved in a non-aqueous solvent such as ethylene carbonate (EC) or propylene carbonate (PC). However, non-aqueous solvents such as EC and PC are volatile and may cause electrolyte depletion during use.
In recent years, therefore, to use a low-volatile ionic liquid as the solvent of a non-aqueous electrolyte has been proposed.
For example, in Patent Literature 1, ionic liquids such as 1-methyl-3-propylimidazolium bis(trifluorosulfonyl)amide and 1-ethyl-3-butylimidazolium tetrafluoroborate are raised as the solvent of a non-aqueous ion conducting medium for air batteries.
A non-aqueous electrolyte air battery is disclosed in Patent Literature 2, in which the non-aqueous electrolyte is a room-temperature molten-salt containing a specific cation and a lithium ion. In this literature, bis(trifluoromethanesulfonyl)amide (TESA), bis(pentafluoroethanesulfonyl)amide, trifluoromethanesulfonylnonafluorobutanesulfonylamide and so on are mentioned as examples of counter ions of the cations.
An air battery is disclosed in Patent Literature 3, comprising a hydrophobic non-aqueous electrolyte containing a room-temperature molten-salt having a melting point of 60° C. or less. In this literature, trimethylpropylammonium bis(trifluoromethylsulfonyl)amide is mentioned as an example of the room-temperature molten-salt.
A lithium secondary battery comprising a non-aqueous liquid electrolyte is disclosed in Patent literature 4. It is not an air battery; however, it uses an ionic liquid as the solvent of the non-aqueous liquid electrolyte, the ionic liquid comprising bis(fluorosulfonyl)amide anion as the anion component.